Hi Kiwipom,
You photo of the 3 rods is interesting. The rod on the right, which I take to be the BSA one, has to my way of thinking, an unusual end cap, in that there is lots of clearance around the nut and a rather sharp looking junction between the face the nut seats on and the face parallel to the axis of the bolt. That junction looks like a stress raiser to me. All the BSA rods I've ever seen before have had a quite narrow circular section milled recess for the nut, with BSA trying to keep as much metal as possible in that area. For that reason I have to use a slimmed down socket to deal with those nuts.
While we're talking about con rods, has anyone any experience of the steel Carrillo ones? Do you need to do a rebalance if you fit them?
JJBSA